Ballistic computer for low-altitude, loft-bombing systems



Feb. 6, 1968 P, G. HUOLT ET AL BALLISTIC COMPUTER FOR LOW-ALTITUDE,LOFT-BOMBING SYSTEMS 6 Sheets-Sheet 1.

Original Filed May 29, 1961 PULL UP RUN IN MAG. NOR TH AIRCRAFT AXISTRACK AIRCRAFT-TO-TARGETJ i INVENTORS PLINY G. HOLT LOUIS S. GUARINODONALD N. SPANGENBERG WALTER GRZYWACZ Feb. 6, 1968 P. e. HOLT ET ALBALLISTIC COMPUTER FOR LOW-ALTITUDE, LOFT-BOMBING SYSTEMS 6 Sheets-SheetOriginal Filed May 29, 1961 u m 0 OH me E VY m 1 L LOUIS S. GUARINQDONALD N. SPANGENBERG WALTER GRZYWACZ HANKSBURG LQJ mzON #362 k wZON mdmFeb. 6, 1968 P. G. HOLT ET AL 3,368,064

BALLISTIC COMPUTER FOR LOW-ALTITUDE, LOFT-BOMBING SYSTEMS Original FiledMay 29, 1961' e Sheets-Shet a r N 61 69-; I

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TRANSVERSE ACCELEROMETER STEERING ANGLE r I l l I I 1 I I l INVENTORSPLINY G. HOLT LOUIS S. GUAFHNO DONALD N. SPANGENBERG WALTER GRZYWACZCURSOR DRIVE Feb. 6, 1968 P. G. HOLT ET AL BALLISTIC COMPUTER FORLOW-ALTITUDE, LOFT-BOMBING SYSTEMS 6 Sheets-Sheet 6 Original Filed May29, 1961 G) (\l N.

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QMRcQQQQQEQ b LOUIS S. GUARINO DONALD N. SPANGENBERG WALTER GRZYWABZUnited States Patent ()fitice 3,368,064 Patented Feb. 6, 1968 3,368,064BALLISTEC COMPUTER FQR LQW-ALTKTUDE, LOFT-BQMBING SYSTEMS Pliny G. Holt,Bethesda, Md, and Louis S. Guarino, Hatboro, and Donald N. Spangenbergand Walter Grzywacz, Southampton, Pa, assigns-rs to the United States ofAmerica as represented by the Secretary of the Navy Original applicationMay 29, 1961, Ser. No. 113,556, now Patent No. 3,136,595, dated June 9,1964. Divided and this application Aug. 27, 1963, Ser. No. 305,017

12 Claims. (Cl. 235-615) AESTRACT OF THE DESCLUSURE A low-altitudeloft-bombing system for high performance aircraft comprising a ballisticcomputer in combination with a navigational dead-reckoning computer foraccurate placement of a bomb over a target. The system compensates forvarious factors, such as run-in speed and altitude, wind and aircraftweight and thrust. Compensation takes the form of corrected steeringangle, variable pull-up point, programmed pull-up and variable bombrelease angle.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

This application is a division of application Ser. No. 113,556 forLoft-Bombing System, by Pliny G. Holt et al., filed may 29, 1961, nowPatent No. 3,136,595.

The present invention relates to a method and apparatus for improvingthe accuracy of low-altitude loftbombing techniques, and moreparticularly to apparatus for providing navigational assistance to thepilot of a high performance aircraft while approaching a bombing targetat a low altitude, for roviding aircraft maneuvering and pull-upguidance to the pilot before release of a bomb, and for providingautomatic release of the bomb to produce precise delivery of the bombabove or on a selected target.

Military requirements for effecting an aerial bombing mission,especially where nuclear weapons are involved, demand that the missilebe delivered at the target with sufficient accuracy to accomplish themission, that an adequate margin of safety from the effects of theweapon blast be rovided for the aircraft, and that the element ofsurprise to the enemy be maintained. Loft-bombing was developed as onetechnique for fulfilling these requirements. The loftbombing techniquebegins with the aircraft on a horizontal approach or run-in toward thetarget at tree-top level to avoid detection by enemy radar. At somediscrete distance from the target, the pilot applies full throttle andpulls back on the control stick thereby pulling the nose of the aircraftup from level flight. This maneuver is called pull-up. When the aircraftlongitudinal axis forms a predetermined angle with the horizontal plane,the bomb is manually or automatically released. The momentum andattitude of the bomb at release causes the bomb to begin its trajectoryupward, and then descend.

One such known loft-bombing technique is partially mechanized in anattempt to reduce the demands on pilot participation and to increase theeffectiveness of a loft bombing mission. On the way to the target, thepilot must recognize a landmark known as the initial point, or IP, whichis of known geographical location with respect to the target. Based oncertain assumed flight parameters for the run-in and pull-up maneuvers,a bombing problem computed prior to the mission begins at the 1P. Sothat the actual flight parameters are consistent with those assumed forthe problem, the pilot must position his aircraft over the IP at a fixedvelocity and course. Upon crossing the IF, the pilot starts a timerwhich measures a precomputed time interval representing run-in distancefrom the IP to a precomputed pull-up point. At the end of the timeinterval, a command signal is presented to the pilot to maneuver theaircraft in a half Cuban eight. At the beginning of the pull'up portionof this maneuver, there is an increase of centripetal acceleration org-loading along the aircraft Z-axis from the lg present at horizontalflight to 4-gs in about two seconds. The g-level transition is madelinear depending upon the best estimate of the pilot as he executespull-up. After the two-second period, the pilot holds the centripetalacceleration at 4-gs until the aircraft completes a little more thanone-half of the loop and then the pilot begins aircraft roll-out. Duringthe pull-up portion, when the aircrafts pitch angle corresponds with apreselected angle, the bomb is automatically released.

The requirements essential for a successful mission utilizing such aloft-bombing technique are numerous. First, there is an extremely highdependence placed upon the accuracy of navigation after positiverecognition of the 1P. Failure to recognize the IP will result in anaborted mission or in an over-thc-shoulder delivery as a last resort.Second, the positioning of a high-performance aircraft flying at lowaltitude over a fixed point, on a fixed course, and at a fixed highspeed requires great skill of the pilot. Third, a constant, high speedrun-in to the target must be maintained. Fourth, the rate of thetransition of g-loading in the two-second period must be consistent withthe precomputed estimates. And fifth, no accumulated errors during theentire bombing maneuver are permissible because the preset bomb releaseangle commits the pilot in advance to the assumed flight parameters.Restated briefly, the known loft bombing techniques allowed for nodeviation from the severe requirements in flight conditions dictated bythose assumed in the precomputed bombing problem.

Accordingly, it is an object of the present invention to provideapparatus for increasing the reliability and accuracy of theloft-bombing technique but at the same time lessen the demands on pilotjudgment, with which variations in the pertinent flight parameters canbe compensated for prior to and during the run-in maneuver of theloftbombing mission, with which the point of start of pull-up followingthe run-in is automatically computed from the pertinent flightconditions existing during run-in, with which the angle of bomb releaseduring pull-11p is automatically computed during the pull-up, and withwhich the transverse acceleration transition during pull-up, isprogrammed based on an on-course distance.

It is another object of the present invention to provide a navigationalaid to the pilot in which the instantaneous position of the aircraft isdisplayed in the cockpit by a cursor and a map each moving in proportionto a computed ground speed and in which synchronization of cursor andmap motion can be corrected at preselected ground check points havingcorresponding marks on the map.

Still another object of the present invention is to provide apparatusfor the computation of guidance information and presentation thereof tothe pilot for steering the aircraft to a desired destination and fororienting the aircraft into a prescribed attitude for pull-up.

And still another object of the present invention is to provideapparatus for low-altitude loft-bombing which employs a visualdead-reckoning type strip-map display of an approach corridor leading toa target and has navigational capabilities, with which the displaycontinuously presents a computed ground position of an aircraft, withwhich the computed ground position accuracy is refined by computeddisplacement and rate corrections, with which reliability ofloft-bombing is further enhanced by the presentation of a computedsteering angle dictating the change in aircraft heading required todirect the aircraft ground track toward the target, and with which thecomputations to effect these presentations requires inputs from trueairspeed, magnetic compass heading, and map display synchronization bythe pilot at two or more preselected ground check points also shown onthe map.

A further object of the present invention is to lessen the demand forpilot acuity by providing apparatus permitting a relatively widelatitude of deviation in approach to the target, with which navigationalaid during approach to the target is improved, with which pull up pointvaries in accordance with variations in certain flight conditions duringthe approach, with which the transverse acceleration schedule isprogrammed during the pull-up, with which visible and audible warningsignals are presented to the pilot for executing aircraft maneuvers, andin which the bomb release angle varies in accordance with ballisticcomputations.

Various other objects and advantages will appear from the followingdescription of one embodiment of the invention, and the most novelfeatures will be particularly pointed out hereinafter in connection withthe appended claims.

In the drawings:

FIG. 1 diagrammatically represents profiles of the flight path of anaircraft and the trajectory of a bomb released from the aircraft on alow-altitude loft-bombing mission;

FIG. 2 represents a strip map of the present invention which depicts atypical approach corridor leading to a target of a loft-bombing mission;

FIGS. 3a, 3b, and 3c schematically represent an approach computer andnavigational display of the present invention;

FIG. 4 diagrammatically represents a top plan view of an aircraft on alow-altitude loft-bombing mission; and

FIG. 5 schematically represents a ballistic computer of the presentinvention.

In the illustrated embodiment of the invention, a lowaltitudeloft-bombing mission is best described with particular reference toFIG. 1. An aircraft approaches the target T from the left beginning on ahorizontal run in path 11 when it crosses the start point S. Theaircraft 10 is maintained at a relatively low altitude to avoid thepossibility of detection by enemy radar until reaching a pull-up point12. The aircraft 10 then takes an insidelooped pull-up path 13 duringwhich the aircraft 10 experiences a transition in centripetalacceleration along its vertical or Z-axis from l-g in horizontal flightto a predetermined higher level. The change in acceleration isprogrammed against distance to the target T, and when the aircraft 10attains a computed upward pitch angle 0 such as at the point 14 on thepull-up path 13, a bomb is released. After bomb release, the aircraft 10continues on the inside loop maneuver and then half-rolling, to directthe aincraft 10 in an upright attitude in the general direction of thestart point S. The bomb, being in free flight from the release point 14,is lofted to an apogee 16 and then it descends toward the target T alongthe trajectory 17.

Several important factors affect the trajectory 17 in a loft bombingmission. One factor is run-in speed. For example, for a constant pull-uppoint 12, an excessive run-in speed will cause a lofted bomb toovershoot the target T while a lower run-in speed may cause the bomb tostrike short of the target T. The present invention contemplatescompensation for different run-in speeds by varying the position of thepull-up point along the run-in path 11.

Another factor is wind. In the consideration of wind. it is convenientto resolve its velocity vector into components parallel and normal tothe length of the approach corridor and hereinafter referred to as rangewind and cross wind, respectively. Each has the effect of decreasingbombing accuracy but in different ways. Range wind has the effect ofdistorting both the pull-up path 13 and the trajectory 17 from what itis in still air. The distortion for a range wind in the same directionas the flight, or a tail wind, is elongation, while a headwind producescompression. The present invention further contemplates compensation forsuch distortions by shifting the pull-up point 12 farther from or nearerto the target T.

Still another factor affecting the trajectory 17 is weight. Duringpull-up, a heavy aircraft moves in a tighter loop and fall-off ofvelocity is relatively fast. The aircraft 10 would also be farther fromthe target T when the release point 14 is reached. Hence, the releaseangle 0 should be decreased for a heavier aircraft to extend the rangeof the trajectory 17. On the other hand, a light airplane moves ii alooser loop and would have a higher velocty at the release point 14since the velocity fall-ofl would not be as great. The aircraft 10 wouldalso be closer to the target T when the release point 14 is reached.Hence, the angle of release 0 at the release point 14 should beincreased for lighter aircraft to shorten the range of the trajectory17.

Available thrust at the pull-up point 14 is another factor which affectsthe trajectory 17. Because of the decrease in thermodynamic efficiencyof an aircraft engne on a hot day, less thrust would be available duringthe pull-up maneuver. The effect of lower atmospheric pressure on thetrajectory 17 is comparable to the effect of higher temperature. Hence atighter loop, less advance down range, and a greater fall-off invelocity results. The added drag resulting from the increased angle ofattack necessitated by a lower atmospheric pressure also lowers the netthrust available. To compensate for the change in thrust, modificationof the release angle 0 accordingly is contemplated.

Finally, there is the factor of run-in altitude. For example, a higheraltitude will produce an overshoot of the bomb relative to the target T.Thus, for higher altitudrs, shifting of the pull-up point 12 fartherfrom the target T is contemplated.

The strip map indicated generally by the numeral 20 in FIG. 2 representsan aerial view of a typical loft-bombing approach corridor from thestart point S to the target T. For purposes of explanation only, andwithout lim'tiag the invention to any specific example, the total lengthof the corridor defined between the start point S and the target T isarbitrarily shown as 60 miles. A mean course line, hereinafteridentified as the MCL, drawn end-to-end and through the center of thecorridor is an arbitrar 1y selected azimuth coinciding with the desireddirection of approach to the target but about which the aircraft 10 maydeviate within the lateral limits of the strip map 20. The 60-mileapproach corridor shown in the map 20 is divided along its length intotwo zones, namely, the FAR ZONE and the NEAR ZONE. The FAR ZONE beginsat the start point S 60 miles from the target T and extends to adistance 15 miles from the target T, then the NEAR ZONE continues to thetarget T. The map scale or reduction in map size in the FAR ZONE isarbitrarily chosen in this embodiment as three times the scale orreducton in map size in the NEAR ZONE.

The map 20 is prepared prior to a loft bombing mission from intelligenceinformation gathered on the area surrounding the target T. There may beseveral maps prepared and loaded in individual cartridges for use in theinvention to cover the eventuality of an alternate approach to thetarget T or even of an alternate target. On a mission, the pilot maycarry several map cartridges from which a selection can be mademomentarily according to the tactical situation encountered.

The target T in the illustrated example is a cluster of storage tanks asshown by the inset circular picture pointed toward the target T.Principal towns, major highways, railroads and rivers are plotted on themap 20 with many minor features and landmarks omitted to avoidcluttering and to facilitate rapid reading by the pilot.

Numerous check points identified by the circled numbers 1, 2, 3, 4 and 5are interspersed along the approach corridor to be used for navigationaland ballistic computations. Accompanying each check point is an insetcircular picture of an object serving as a precise point of reference inthe approach corridor. The object at each check point is selected forits easily recognizable features and has a known position with respectto the target T.

The map 20 contains several additional visual aids for the pilot. Besideprincipal terrain and geograph'cal features, there are tick marks alongthe MCL designating on-course distances to the target T. Beginningaround the 45-mile tick mark, there is a shaded area 21 on each side ofthe map 20 to warn the pilot of a pending change of map scale and anarrowing of the approach corridor. It is necessary for the pilot tonavigate the aircraft between the shaded areas 21 by the time that the-mile tick mark is reached when the map changes scale. In the NEAR ZONEthere are two curved lines 22 symmetrical about the MCL and beginning atopposite sides of the map 20 about 9 miles from the target T. The curvedlines 22 form a funnel-like area narrowing toward a pullup region 23,shown shaded. The curved lines 22 represent limits from which the pilotcan still maneuver the aircraft 10 into position for pull-up byexecuting two standard rate turns, i.e. the rate of change in headingneed not exceed 3 degrees per second. The pull-up region 23 representsthe on-course limits for ballistic computations and lateral tolerances.The size of the pull-up region 23 is indicative of the degree offlexibility provided by the invention for the execution of aloft-bombing mission.

The map 20 is displayed in the aircraft 10 on a cartridge insertable ina display unit 26, as shown in FIG. 3c, and is transported by a sprocketroller 27 in a direction parallel to the MCL. The map 20 has punchedholes 28 spaced along each side for engaging spurs in the sprocketroller 27. A roller knob 29 fixed at one end of the roller 27 providesmanual slewing of the map 20 to any desired position along the MCL. Itis contemplated that map slewing may also be accomplished electricallyby additional push buttons and electrical relays.

A transparent cursor 31 in the display unit 26 provides a continuousindication of the lateral position of the aircraft 10 in the approachcorridor. The cursor 31 has a vertical index 32 inscribed thereon withtick marks spaced at intervals corresponding to each of the scales ofthe map 20. A transparent bar 33 fixed against motion on the dis playunit 26 in front of the map 20 has a horizontal index 34 inscribedthereon with appropriately spaced tick marks. The point on the map 20under the intersection of the vertical and horizontal indices 32 and 34is a computed instantaneous map position. The cursor 31 is drivenlaterally by means of a worm gear 36 which is rotatably supported at itsends in the display unit 26 by means not shown.

NAVIGATION COMPUTATIONS The point on the map which appears at theintersection of the vertical and horizontal indices of the display unit26 is determined by navigational computations which may be categorizedgenerally as on-course and cross-course computations. The on-coursecomputation determines the position of the map along the MCL withrespect to the horizontal index 34. The cross-course computationdetermines the position of the cursor 31 along the horizontal index 34relative to the MCL.

Orr-course map drive The on-course computation mainly consists of anintegration of true airspeed TAS which yields an on-course distancemeasured from the start point S. The TAS input is derived from atransducer 37, such as a Pitot tube having its pressures transformedinto an angular position on a shaft 38. The shaft 38 is connected to oneinput of a mechanical differential 39. If the other input to thedifferential 39 is locked, the output shaft 41 is also proportional tothe TAS and positions the rotor of a linear transformer 42 in a mappositioner unit 40. A linear transformer, as used herein, has thecharacteristic of generating an output voltage whose magnitude is alinear function of an input shaft position. The output voltage oftransformer 42 is connected to an on-course integrator comprising acombination of a motor 44, a generator 46 and an amplifier 47. The otherinput of the differential 39 being locked, the position of a shaft 48between the motor 44 and the generator 46 is a time integral of the TAS.The shaft 48 also connects to the rotor of a synchro transmitter 49 of amap drive unit 56 through one input of a mechanical differential 52 anda differential output shaft 53. Depending upon the position of a scalechange switch 57a operated by a cam 57 driven by the shaft 61 when themap 20 indicates the aircraft position is 15 miles from the target T,either a FAR ZONE synchro receiver 56 or a NEAR ZONE synchro receiver 54will supply a voltage to an amplifier 58 to drive a map drive motor 59.An output shaft 61 of the motor 59 is selectively connected to thesprocket roller 27 in the map display unit 26 through a clutch 62 whichis engaged when the map 20 is inserted. The shaft 61 is also coupled tothe rotors of the receivers 54 and 56 thus providing a continuousfollow-up of map position through the receiver 54 or 56 as determined bythe switch 57a. The coupling between the rotor of the receiver 54 andthe shaft 61 includes gears 63, so that the map drive rotor 61 isrequired to drive through three times the angular displacement of theshaft 53 in order to follow-up a given increment of error voltage at theamplifier 58. This corresponds to the map scale change.

Due to the presence of a range wind, an error will accumulate betweenthe actual ground position of the aircraft i0 and the position indicatedon the map 20 inasmuch as TAS measurement is not a measurement of groundspeed of the aircraft. In order to align the map position with aircraftposition relative to the ground and synchronize the map drive speed withaircraft ground speed, several adjustments are necessary to the shaft 53at the input of synchro transmitter 49 of the map drive unit 50. One ismodification of the shaft 48 at the output of the map positioner unit 40in the form of a step correction. The step correction periodicallyrepositions the map '20 so that a point under the horizontal index 34corresponds with the actual position of the aircraft over the ground inthe approach corridor. Another is a modification of the shaft 38 at theinput of the map positioner unit 40 in the form of a rate correction.

Orrcourse step correction Step correction is a periodic skipping of themap 20 either in the forward or reverse direction. This occurs at anytime there is a lack of agreement between the position of one of thecheck points 1, 2, 3, 4 or 5 relative to the horizontal index 34 and thelocation of a corresponding object on the ground at the time the pilotmakes a visual comparison and effectuates synchronization. A stepcorrection unit 60, operating independently of rate correction, and inboth the NEAR and FAR ZONES, restores alignment. At an on-coursedistance of two miles before and after each check point called theenabling zone, an electrical enabling switch 67 fixed on the displayunit 26 operates. The switch 67 has two opposing contacts held apartbecause they extend on the opposite surfaces of the map 20.Corresponding to precisely 2 miles before each check point 1, 2, 3, 4and 5 on the map 20, there is a hole 68 laterally aligned with thecontacts of the enabling switch 67. When the map 20 moves so that one ofthe holes 68 is between the contacts of the enabling switch 67, thecontacts close and cause a solenoid operated clutch 69 to engage therebycausing the rotation of the map drive output shaft 61 to be transmittedto the rotor of a linear transformer 66. By appropriate relays, contact67a also moves from the position illustrated to connect transformer 66in series with a linear transformer 76 and an amplifier 71. As map driveprogresses, an output voltage of the transformer 66 appearing at theamplifier 71 and representing a distance error, decreases from a presetlevel at the step correction enabling position (2 miles before the checkpoint) to zero at the check point and then increases in the oppositedirection to the same level at the step correction disabling position (2miles after the check point). A motor 72 driven by the amplifier 71 hasits output shaft 73 selectively connected to another input of themechanical differential 52 through a solenoid operated clutch 74.Positive positioning of the motor 72 is accomplished by follow-up of thelinear transformer 76. The clutch 74 is disengaged while the distanceerror is accumulating on the output shaft 73. The pilot depresses a MARKbutton 77 located on the'display unit 26"when he observes that theaircraft 10 is abreast of a check point. By an electrical circuit, notshown, a contact 77a in the step correction unit 60 moves from theposition illustrated to connect the transformer 76 as the sole input tothe amplifier 71, and the motor 72 will drive until the transformer 76has been restored to its position at the start of step correction. TheMARK button 77 also causes clutch 74 to engage so that the restoringrotation appearing on the shaft 73 is transmitted to the other input ofthe mechanical differential 52. The input on shaft 48 to thedifferential 52 is thus periodically corrected by the increment ofrotation entered through the shaft 73. Depressing the MARK button 77also disengages the clutch 69 previously engaged by the switch 67. Camswitch 70 will disengage the clutch 69 at the end of the enabling zoneif the MARK button 77 is depressed at a check point. A fly-back spring79 restores the rotor of transformer 66 to the step correction enablingposition.

Summarizing step correction, when the aircraft 10 comes abreast of eachpreselected check point the MARK button 77 is depressed. If, at thatinstant, the on-course component of the map position does not agree withthat of the geographical position of the aircraft 10, that is, if thecorresponding check point on the map is not under the horizontal index34, the map will skip due to the restoring motion on the shaft 73 anamount sufficient to align the map with the geography. It should benoted that failure to depress the MARK button 77 within the enablingzone will not be harmful to the accuracy of the existing map alignment.Tracking will continue in accordance with the corrected informationaccumulated up to the previous check point.

Step correction can be made in both the NEAR and FAR ZONES. Alocked-rotor linear transformer 81 in the step correction unit 64 havinga voltage transformation ratio corresponding to the change in map scaleis selectively connected in the circuit with transformer 66 by contacts57b which are operated at miles from the target T by the cam 57.

Oil-course rate correction On-course rate correction refers to thedifference or error between the map drive rate and the actual aircraftground speed. So that the drive rate is accurately synchronized with theground speed of the aircraft 10 is accomplished before the aircraft 10reaches the NEAR zone, this error must be taken into account. In effect,the oncourse rate error, prior to any correction, is the differencebetween the true airspeed TAS and ground speed. This difference oron-course rate error is added through the other input of the mechanicaldifferential 39 to modify the TAS signal on shaft 38 whereby theposition of the output shaft 41 is a corrected TAS corresponding to theoncourse ground speed. The on-course rate correction is computed withinthe enabling zone by an on-course rate correction unit 90.

To obtain the correction rate, an increment of map transport distance isdivided by the time from start point S. A timer 86 produces a positionon a shaft 87 which is a function of time from the start point S. Theshaft 87 drives the rotor of a linear transformer 88 through a solenoidoperated clutch 8'9. Clutch 89 is engaged at the start of the run-inwhen a START button 8%} is depressed. At the beginning of the enablingzone (2 miles before each check point in the PAR ZONE) when the enablingswitch 67 engages the clutch 69, map motion is transmitted through theoutput shaft 61 to the rotor of a linear trans former 95. Within theenabling zone a contact 6711, operated by the enabling switch 67,connects the electrical output of the linear transformer 88 to the rotorcoil of a linear transformer 91. The fixed coil of the transformer 91 isconnected in se ies with a contact 670, operated by the enabling switch67, to the fixed coil of the transformer 95, and an amplifier 92. Theresulting voltage at the amplifier 92 is proportional to the quotient ofthe electrical sign l devel p d yi ransfcrmersfls and 9 pp p iat scalefactoring is provided by the locked rotor of the linear transformer 94which has its electrical output connected to the rotor coil oftransformer 95. A motor 93 is driven by the amplifier 92 accordinglypositioning an output shaft 96. Follow-up for the shaft 96 is providedby its connection to the rotor of the transformer 91. The angularposition of the shaft 96 at any instant within the enabling zone isrepresentative of the instantaneous rate error which is the negative ofthe amount that would be necessary to correct the map drive rate; andwhen the pilot depresses the MARK button 77 in an enabling zone, acontact 77!) disconnects transformer 95 and leaves transformer '91 asthe sole input to the amplifier 92. Simultaneously, a solenoidoperatedclutch 97 engages the shaft 96 to the other input of the differential 39through a shaft 96a. As the motor 93 restores the rotor of transformer91 back to the null position, the restoring rotation of the shaft 96 istransmitted through the clutch 97 to the differential 39 where itmodifies the TAS input on the shaft 38 as appears on the shaft 41 to themap positioner unit 40. In a manner described above, clutch 69disengages at the end of the enabling zone, and the fly-back spring 79restores the rotor of transformer 95 to its initial position. Similarly,at the end ofa loft-bombing mission the clutch 89 disengages and afly-back spring 98 restores the rotor of transformer 88 to its initialposition.

It will be noted that on-course rate correction is provided for onlywithin the PAR ZONE, whereas step correction is accounted for in boththe NEAR and FAR ZONES.

Cross-course cursor drive To facilitate an understanding of the anglesrelated to cross-course navigation, particular reference will be made toFIG. 4. A medial line identified as a mean course line or MCL on the map20 corresponds to a magnetic rhumb line extending end-to-end along theapproach corridor to the target T. Due to the presence of thecross-course component of wind and due to the probable lateraldisplacement of the aircraft 10 from the MCL, various angles can bedefined. For a lateral displacement y, a target angle 7 is formed by anaircraftto-target line and the MCL. Assuming a cross wind component fromthe left side of the approach corridor, or downward in FIG. 4, theaircraft 16 must take a port heading. The angle 7 formed by thelongitudinal axis of the aircraft i0 and the MCL is the aircraft headingrelative to the MCL. The path of the aircraft 10 actually taken over theground is called the ground track and defines a course angle a with theMCL. The difference between the heading angle 1 and the course angle 06is a drift angle 5 and the angle formed by the ground track and theaircraft-to-target line is the steering angle 1.

The distance the aircraft 10 is from the target T along theaircraft-to-target line is the actual distance-to-go, For small targetangles 7', the actual distance-to-go is substantially equal to theoncourse distance-to-go as measured along the MCL.

The cross-course cursor 31 position is the result of integration of across-course component of the ground speed from an initial lateralposition of the lateral cursor 31 to a subsequent lateral position. Theinitial position is considered as a constant of integration for thepurpose of computation. The product of the TAS and the course angle oris further considered to be a close approximation of the cross-coursecomponent of ground speed because, for small course angles a, the sineof a is substantially equal to the angle a in radians. Inasmuch asnavigation within the approach corridor usually involves course angles awhich are less than 15 degrees, this approximation of the sine can bemade without significant loss in accuracy.

The cursor 31 in the display unit 26 continuously tracks the lateralposition of the aircraft by means of a cursor drive unit 160 (FIG. 3c).True airspeed TAS, appearing as an angular position on shaft 33 isconnected to the rotor of a linear transformer 101. The output voltageexcites the rotor coil of a linear transformer 192 which has its rotorpositioned by a shaft 1115 which is angularly positioned as a functionof the course angle or. The manner in which the course angle or isobtained on the shaft 165 will be described below in connection withdrift correction. The output voltage developed in the fixed coil of thetransformer 1112 thus becomes the product of TAS and the course angle orwhich is substantially the cross-course component of ground speed. Thisvoltage is fed to the cross-course integrator which includes a generator103, an amplifier 194, and a motor 166. An output shaft 197 of the motor106 is positioned as a function of a time integral of the cross-courseground speed, namely, the cross-course distance. The position of shaft167 is then transformed into an electrical voltage by means of a lineartransformer 108. The output voltage of the transformer 108 is connectedthrough contacts 88a and 88c in series with linear transformers 1&9 and112 across an amplifier 111 when the START button 30 is depressed. Theamplifier 111 drives a cursor drive motor 113 which is drivinglyconnected to the worm gear 36 by an output shaft 114. The shaft 114 isalso coupled to the rotor of the linear transformer 109 for follow-upaction. The motor 113 continues to drive until the change in outputvoltage of the transformer 1139 is equal and opposite to the change inoutput voltage of the transformer 108. The position of the shaft 114 istherefore representative of the cross-course distance traveled duringthe integration. Another pair of contacts 8%, operated by the STARTbutton SQ, are maintained in the position illustrated until the aircraft11] is abreast of the start point S. This is so that cursor 31 can beplaced at a given initial lateral displacement from the MCL and somaintained until integration is desired.

For establishing the lateral position of the vertical index 32 relativeto the map 211 so that it corresponds to the lateral position on theground throughout the run-in, it is necessary to set the vertical index32 on a corresponding ground reference point from which the distanceintegration is started. This is accomplished by the linear transformer112 which provides for manually setting the initial lateral cursorposition, or subsequent lateral positions. From a mathematicalstandpoint, the setting may be regarded as fixing the constant ofintegration. Manual setting of the cursor is made at any time by acursor adjusting knob 116 which turns the rotor of the transformer 112through a shaft 117. Manual adjustments can also be made prior todepressing the START button 80 whereby contacts 80a and 80b remain inthe positions illustrated. Thus, transformers 109 and 112 are the onlyinputs to the amplifier 111. The position of the shaft 114 thereforecorresponds to the lateral position selected on the knob 116. When theaircraft 1G is over the ground reference point, the START button 80 isdepressed whereby contacts 80a, 80b and 80c enable rotation of the shaft114. At miles from the target T, a linear transformer 118 having alocked rotor has the output of its fixed coil connected to the rotorcoil of transformer 109. The rotor of transformer 118 is locked in aposition which yields a transformation ratio equal to the scale changefrom the FAR ZONE to the NEAR ZONE.

Drift correction The course angle or appearing as an angular position onthe input shaft of the cursor drive unit is computed by algebraicallyadding the heading angle 11 and the drift angle 6. The latter iscomputed in a drift angle unit 1211 by components of a lateral error dueto a cross wind and the on-course distance over which the lateral erroraccumulated. The lateral error, which is the crosscourse distance inmiles between one point on the map 20 corresponding to the actual groundposition of the aircraft 10 and another point on map 20 indicated by thevertical index 32, is manually introduced in the drift angle unit at theknob 116 connected by the shaft 117 and a solenoid operated clutch tothe rotor of a linear transformer 124. The positioning of the verticalindex 32 is based solely on the best estimate of the pilot. The outputvoltage of the transformer 124, proportional to the lateral error, isconnected to the one stator coil of a resolver 126. The second statorcoil of the resolver 12-6, in quadrature with the first stator coil, issupplied by the output voltage from a linear transformer 127. Theangular position of the output shaft 61, representing the oncoursedistance since the previous lateral check point, is connected to therotor of the transformer 127 through the solenoid operated clutch 128.The clutches 125 and 12-8 are engaged by depressing the START button 89thereby transmitting the angular positioning of shafts 61 and 117 to thetransformers 127 and 124, respectively. The resolver 126 has one of itsrotor coils (not shown) short circuited, while the other rotor coil isconnected to the input of an amplifier 129 which drives a motor 131 whencontacts 80d, operated by the button 80, move from the positionillustrated to the opposite position. An out put shaft 132 of the motor131 provides a follow-up connection between the rotor of the resolver126 and the motor 131. The angular position on the shaft 132 thereforeis the negative of the drift angle 6 whose tangent is the lateral errordivided by the on-course distance in which the lateral error wasaccumulated.

A DRIFT button 122, located on the display unit 26, is depressed when aselected lateral reference is reached. Clutches 125 and 128 disengageallowing fly-back springs 123 and 123a to restore the rotors of thetransformers 124 and 127 to their initial or zero position. Contacts122a then move from the position illustrated to the opposite positionallowing the motor 131 to drive the resolver 126 back to its initial orzero position. A normally engaged clutch 133, which disengages when theSTART button 80 is depressed and permits shaft 132 to be positioned bythe inputs of shafts 117 and 61 Without affecting a mechanicaldifferential 134, reengages when the DRIFT button 122 is depressedthereby transmitting the restoring rotation of the shaft 132 to oneinput of the differential 134.

The drift angle unit 120 also includes an option for the pilot to set anestimated cross wind into the system prior to the start of the run-in ofa bombing mission. A CROSS WIND knob 148 positions the rotor of a lineartransformer 149 having a stator coil of a linear transformer 151,contacts 80d in the position shown, and the amplifier 129 to drive themotor 131. Being normally engaged by the clutch 133 prior to start, theshaft 132 drives the transformer 151 until a voltage has been developedin the stator coil of the transformer 151 which is equal and opposite tothe output voltage of the transformer 149. The position of the shaft 132thus represents the initially estimated cross wind as a drift angle 6,at an assumed on-course TAS. After the START button 80 is depressed, theelectrical circuit in the drift angle unit 120 is changed so that manualsetting of cross wind is no longer operative. Initially, the transformer151 is rotated to a position which is representative of the initialcross wind drift angle.Clutch 133 is disengaged when the START button 80is depressed and is engaged at the completion of the drift computation.It will be noted that successive 1 1 drift solutions are added to theinitial cross wind drift angle existing on the transformer 151 and arestored for future use.

The drift angle 6 at the shaft 132 is combined with an aircraft heading1 relative to the MCL at the mechanical differential 134. If more thanone increment of drift angle has been computed, the correcting quantityat the differential 134 is a summation thereof.

Course angle A heading unit 140 computes the aircraft heading withrespect to the MCL. Map angle (FIG. 4) with respect to North and localmagnetic variation angle 5 at the target T are set into the heading unit140 by means of adjusting knobs 137 and 138, respectively. The summationof these two quantities takes place in a mechanical differential 139with its output shaft 136 representing the magnetic azimuth 5 of theMCL. The rotor of a differential generator 141 is coupled to the shaft136 and is continuously excited by a signal from a magnetic compass 145in the aircraft 10. The output signal of the generator 141 is thedifference between the magnetic heading ,1 and the magnetic azimuth [3of the MCL, or the aircraft heading 1 with respect to the MCL. Theheading 1 is then transmitted to a control transformer 143 which has itsoutput voltage connected to an amplifier 144 which in turn drives amotor 146. The shaft 147 of the motor 146 is mechanically coupled to therotor of the transformer 143 to provide follow-up. Thus, the angularposition of the shaft 147 is representative of the aircraft heading 1;with respect to t the MCL. For a no-drift condition, this angle 1 isalso the course angle oz. The heading 1 on shaft 147 and the drift angle6 on shaft 132 are algebraically combined in the differential 134 toproduce the course angle a on the shaft 105. As noted previously, thecourse angle a modifies the T AS signal on shaft 38 in the cursor driveunit 100 to obtain the cross-course speed component for driving thecursor 31.

' Steering angle The above-described mechanisms provide a display on themap 20 of the aircraft 10 instantaneous position relative to ground bythe intersection of the horizontal index 34 and the vertical index 32within the approach corridor to the target T. The line generated by themovement of the instantaneous position is called a ground track. Anadditional important navigational aid to the pilot is a steering angle a(FIG. 4). The steering angle a enables the pilot to direct the groundtrack of the aircraft 10 toward the target T, so that the ground trackcoincides with the aircraft-to-target line. The steering angle 0' isderived by a steering angle unit 160 using as inputs, the lateraldistance y from the MCL, the on-course distance to the target T, and thecourse angle a. The on-course distance to the target T is introduced bydisplacing the rotor of a NEAR ZONE linear transformer 156 and a FARZONE linear transformer 157 an amount equal to the scale distance fromthe target T to the start point S. This may be accomplished by firstinserting the map 20 into the display unit 26 so that the target T liesunder the horizontal index 34, engaging the clutch 62, and then slewingor transporting the map 20 manually by the knob 29 until the start pointS lies under the horizontal index 34. Because the clutch 62 is engaged,the rotors of the transformers 156 and 157 will rotate by theirconnection through the shaft 61. This operation stores adistance-to-target in the rotor position of the transformers 156 and157. As the aircraft approaches the target T along the approachcorridor, the map drive motor 59 is continuously reducing the value ofthe stored distanceto-target. The output voltage of the transformers 156and 157 are selectively supplied the first stator coil of a resolver 159through a contact 57] operated by the map scale changing cam 57 at milesfrom the target T. The electrical signal applied to the second statorcoil, in quadrature with the first, comes from the output of a lineartransformer 161 which has its rotor positioned by the shaft 114 from thecursor drive unit 100, and therefore represents the lateral displacementy from the MCL. One rotor coil (not shown) of the resolver 159 isshortcircuited, while the other rotor coil supplies a voltage to anamplifier 162 which drives a motor 163. The motor 163 is mechanicallycoupled to the rotor of the resolver 159 by a shaft 164 forpositive-positioning follow-up. The resulting angular position of theoutput shaft 164 represents a target angle 1- whose tangent is thequotient of the lateral distance y from the MCL divided by the on-coursedistance to the target T.

The target angle 7' and the course angle a are the inputs to amechanical differential 166 which algebraically combines the courseangle at and the target angle -r, the output on a shaft being thesteering angle 0'. If the course angle a equals the target angle r, inboth magnitude and direction, the ground track of the aircraft 10 passesthrough the target T. If the two angles are not equal, the differencerepresents an angle which the pilot must apply as a steering correctionin order to direct the ground track of the aircraft toward the target T.The steering angle 0' is converted into an electrical signal by apotentiometer 167 and is displayed to the pilot on a vertical pointer168 of a cross needle indicator 170. It should be noted that thesteering angle 0' is merely a reference. The pilot may deviate theaircraft 10 laterally along the approach corridor to suit conditions ofthe bombing mission. Only during the last portion of runin, that isimmediately prior to the pull-up point 12, must the steering angle a becorrected so that the aircraft ground track coincides with theaircraft-to-target line. At one-third of a mile before the pull-up point12, a G-start selector switch 171 moves from the position illustrated todisconnect the steering angle unit 160 from the indicator and to connectthe output from a yaw/ roll unit 175. The shaft inputs 173 and 174 tothe unit 175 represent yaw and roll signals from gyros in the aircraft10 and by the arrangement of potentiometers in the unit 175, a combinedroll and yaw signal is connected to the indicator 170 to producedeflection of the vertical pointer 168 during pull-up. The indicator-170also includes a horizontal pointer 176 electrically connected to apotentiometer 177 which is varied by a mechanical output of anaccelerometer 178. The accelerometer 178 is responsive to accelerationthrough the transverse axis or Z-axis of the aircraft 10.

BALLISTICS COMPUTATIONS The ballistic system of the present invention isprincipally a mechanical analog computer integrally a part of thenavigational computer system, sharing its components and utilizing camsto solve the bombing problem. The navigational system as above-describedprovides a convenient stepping stone leading to a coordinated ballisticcomputation system insofar as it provides the necessary parameters forcomputing a variable pull-up point and a release angle for the bomb inthe bombing problem. The availability of these parameters in thenavigational system of the present invention allows the solution of theballistic problem with only small structural additions. For example,navigational computation of the distanceto-target, together with TAS,can determine a variable pull-up point; and a parameter of range windpermits further refinement of the pull-up point.

Prior to reaching the pull-up point 12, a range wind correction and astill air pull-up distance are developed and combined to obtain apull-up point which will vary in accordance with the input parameters.After the pullup point 12, the g-level transition in the pull-upmaneuver is programmed for the pilot and the bomb release angle isautomatically computed in accordance with the errors accumulated fromthe pull-up point 12 to the release point 14. In this manner, the loftedbomb will be precisely delivered on the target T.

"'5 1; Range wind correction The range wind correction is a computeddistance which serves to correct the still air pull-up distance from thetarget T. It is the product of the total time anticipated from thepull-up point to impact multiplied by the range Wind velocity or thetotal on-course rate correction accumulated in the PAR ZONE. Incomputing the range wind correction, it is assumed that the air moveswith the same speed and direction at all altitudes.

The total on-course rate correction developed by the the unit 90 at itsoutput shaft 96a angularly positions the rotor of a linear transformer179 of a range wind correction unit 181 The output voltage excites alinear transformer 182 when contacts 570, operated by the cam 57, closeat the beginning of the NEAR ZONE. Since the total time is a function ofa particular run-in speed, TAS is used as an input to a total time cam183. The rotor of the transformer 182 is angularly positioned by thetotal time cam follower thereby developing a voltage on the fixed coilof the transformer 182 proportional to the product of the total time andthe accumulated on-course rate correction. This voltage is impressedacross the am plifier 92 and the stator coil of the transformer 91 whenthe contacts 57c close. The amplifier 92 thus drives the motor 93, shaft96 and the rotor of the transformer @1 until the latters output voltageis equal to and opposite that eXisting on the rotor coil of thetransformer 182. The resultant position of the shaft 96 is thereforeproportional to a distance which is the range wind correction.

Pull-up point and G-programmer The shaft 96 is also mechanically coupledto one of the inputs of a mechanical differential 184 (FIG. 5). Theother input to the differential 134 is the angular position of thefollower of a still air distance cam 186. This shaft position predictsthe pull-up distance from the target T for a particular run-in speedunder a still air condition. The algebraic sum of the two inputs to thedifferential 184 is a corrected pull-up distance from the target T for aparticular speed and range Wind condition and is represented by theangular position of the shaft 187.

The shaft 187 from the differential 184 is connected to one input of amechanical differential 183 where its position is subtracted from theinstantaneous map position represented by the angular position of theshaft 61 connected to another input of the differential 188. The outputshaft 189 of the differential 138 therefore represents the remainder ordistance to go to pull-up and is used for generating various alertingsignals. A cam 191 rotates with the output shaft 189 causing a contact192 to close momentarily at one mile and at two-thirds of a mile beforethe pull-up point thereby energizing a green warning light 193 as avisual indication to the pilot of approach to the pull-up point 12. Asignal is also initiated by a g-start cam 185 which rotates with theshaft 189 and engages the solenoid operated clutch 193 of a gprograrnmerunit 190 at the point one-third mile from the pull-up point. As notedpreviously, switch 171 (FIG. 30) also moves from the position shown.Shaft 61 now drives a plurality of cams. A switch cam 199 connects a DC.electrical source to a potentiometer 201. A g-cam 197 rotates with theshaft 61 with its follower connected to the wiper arm of thepotentiometer 201 which in turn has its variable output voltageconnected to the drive coil of a horizontal pointer 176 in the indicator170. The potentiometer 201 output is characterized to cause the pointer176 ffr'st to drop, then to rise gradually, and finally to reach ahorizontal position at the precise instant of the computed pull-up point12. This pointer action provides a visible anticipatory signal forpull-up. At the point of pull-up, a cam 202, driven by the shaft 61,closes a contact 203 to connect a DC. electrical source to an audiooscillator 204 and a pull-up light 206; and the gprogrammer cam 197continues to rotate to drive the pointer 176 according to a desiredschedule of transition from one g to four gs transverse accelerationalong the Z-axis of the aircraft 10. The output signal from thepotentiometer 2111 opposes the output signal from the potentiometer 177at the actuating coil of the pointer 176 thereby presenting aninstantaneous gerror signal on the pointer 176. The g-transitionschedule is therefore a function of the on-course distance to the targetT, and the acceleration program throughout this distance may be variedto meet any tactical condition. For example, an S-shaped pull-up curveor acceleration versus distance curve is preferred in certainhigh-performance aircraft. When the pilot maneuvers the aircraft 10 sothat the transverse acceleration along the aircraft Z-axis matches theoutput of the potentiometer 201, the pointer 176 remains horizontal,indicating that the proper pull-up maneuver is being executed. Anydeviation from the gprogram is indicated by a deflection of the pointer176 which the pilot can correct with the control stick. Earphones Zfilare provided for presenting the audible signal from the oscillator 294to the pilot. After release of the bomb, the clutch 193 is disengagedand a fly back spring 268 resets the cams in the g-programmer unit toits initial position prior to pull-up.

Bomb release angle As noted earlier with reference to FIG. 1, therelease angle 0 should be varied to correct for errors developed afterthe computed pull-up point. A bomb release angle unit 2141 is providedfor computing the variable release angle 0 based on deviations from thepredicted fall-off of velocity during the pull-up. At the beginning ofpull-up, determined by the pull-up cam 2412, solenoid operated clutches211 and 213 engage. The clutch 211 drivingly connects the timer outputshaft 87 to a differential velocity or AV cam 212 whereby it isangularly positioned in proportion to integrated time from the pull-uppoint. The shape of cam 21?; produces follower motion representing thepredicted fall-off of aircraft velocity at any instant of time duringthe pull-up. The clutch 213 drivingly connects the TAS shaft 38 througha shaft 38a to one input of a mechanical differential 214. The positionof shaft 330 is not true airspeed, but the actual velocity fall-off;i.e. the difference between true airspeed and the instantaneous value oftrue airspeed at the computed pull-up point upon closing the clutch 213.The other input to the differential 21 i is connected to the follower ofthe AV cam. The output shaft 216 of the differential 214 therefore isthe difference between the predicted velocity fall-off as generated bythe cam 212 and the measured velocity fall-off at any instant after thecomputed pull-up. If the measured velocity fall-off and the predictedvelocity fall-off are the same, the output of the differential 214 iszero and no change in the preselected release angle 0 is necessary.However, if they differ, the shaft 216 causes rotation of a At) cam 217.The follower of the A19 earn 217 develops a quantity proportional to amodification in the preselected release angle 0 required to obtain atarget hit. The follower motion is transmitted to one input of amechanical differential 223, the other input being a preselected releaseangle 6 adjusting knob 224. The output shaft 226 of the differential 223is drivingly connected to one input of a mechanical differential 227where it is compared with another input 228 from a vertical gyro 229.The algebraic sum of these inputs appears at the output shaft 231 whichrotates a bomb release cam 232. At the precise modified bomb releaseangle (Riot), the cam 232 closes a contact 233 connected in series witha pickle switch 236 and an electric mechanism 234. If the pilot-actuatedpickle switch 236 is closed at the time the contact 233 closes, themechanism 234 will release a bomb 237.

OPERATION The pilots role in a low-altitude, loft-bombing missionutilizing the present invention is a vital one because he is the linkwhich ties the computations and input data to geographical landmarks andhe also is the link between the output information and the aircraftperformance. Certain inputs such as TAS and magnetic heading areautomatically entered into the system without attention from the pilot;but the on-course and cross-course corrections are supplied by the pilotas he ties in specific points in the computations to the geographicallandmarks. The display unit 26 provides a means by which the pilot canmonitor the end result of the navigational computations. The outputinformation is essentially guidance instructions or commands which reachthe pilot by visible or audible signals. The indicator 170 providessteering guidance up error and g-error information for the pull-upmaneuver. Warning lights and a pull-up tone provide timing informationto the pilot of guidance events.

Prior to a bombing mission, the strip map 20 is prepared based onintelligence information developed from reconnaissance information abouta target area. The map 20 is then loaded on a cartridge in the displayunit 26. The map angle A and local variations are entered by theadjusting knobs 137 and 138, respectively. The map 20 is then aligned sothat the target T lies directly under the horizontal index 34. Theclutch 62 is then engaged and the pilot slews or transports the map 20by means of the roller knob 29 until the start point S lies directlyunder the horizontal index 34. This stores the total distance to thetarget T in the steering angle unit 160. If the pilot has an estimate ofthe cross wind, he has the option of setting this value into the driftangle unit 120 with the cross wind adjusting knob 148. These settingsare possible at any time before arrival at the start point S, afterwhich the system is ready to begin a bombing mission.

Referring to the map 2t) in FIG. 2, the low-altitude loft-bombingtechnique will be further described. When the start point Scharacterized by a large three-wing multistory building first comes intoview from the aircraft flying toward the target area, the pilot adjuststhe cursor adjusting knob 116 of the drift angle unit 120 to thepredicted lateral distance from the start point S at which the aircraft19 will be when it flies abreast of the start point S. For example, 16miles to the left of the start point S, as represented by a typicalground track 238 on the map 20. Although it is preferable to have thepredicted lateral distance setting made prior to the arrival abreast ofthe start point S, there is about a l-mile leeway allowed beyond thestart point S in which interval the initial setting could still be made.When the aircraft 10 comes abreast of the start point S, the pilotdepresses the START button 80 to start the map motion and computeroperation. From this point on, the pilots task is to establish goodcomputer tracking.

When the aircraft comes abreast of each preselected ground check point1, 2, 3, 4 and 5, the pilot marks the aircraft 10 position by depressingthe MARK button 77. If the on-course component of the map position doesnot agree with that of the geographical position of the aircraft 10 atthat instant, that is, if the check point printed on the map is notunder the horizontal index 34, two types of corrections occur. One isthe step correction or skip of the map which brings the on-coursecomponents of the map position into alignment in both the NEAR and FARZONES. The other is the on-course rate correction which synchronizesaircraft speed in the PAR ZONE with the map speed. After about threemarks in the FAR ZONE, correct on-course tracking is established. Asnoted before, an inadvertent omission of a mark at any of the checkpoints is not harmful to the accuracy of the computation. Trackingcontinues in accordance with the corrective information accumulated upto the last marked check point.

From the start point S, tracking in the cross-course direction dependsupon the initial lateral setting of the to one-thirdrmiler from pull-up;and thereafter, yaw/roll if cursor 31, the estimated cross windssetting, and the automatic inputs of the compass and TAS transducer 37.Corrected cross-course tracking is subsequently added. There being nopreselected lateral check points, the pilot selects his own. A straightsection of railroad or highway running in the same general direction asthe line of flight makes an excellent lateral check point. For example,in map 20 the substantially parallel portion of highway between 50 and52 miles from the target T in the PAR ZONE is estimated as 7 miles tothe right of the aircraft 10 within that region. The pilot adjusts thecursor adjusting knob 116 so that the cross-course component of the mapposition agrees with his estimated geographical position, and thenpresses the lateral drift button 122 thereby entering alateralcorrection into the drift angle unit 120. The drift angle 5 iscomputed and is further combined with the heading 1 to obtain thetracking as described above. After about two such lateral estimates inthe PAR ZONE, correct tracking in the lateral direction is established.

The shaded area 21 on the map 20 alerts the pilot to an impending changein map scale. The aircraft 10 must not be tracking in the area 21 whenthe map 20 changes from the PAR ZONE scale to the NEAR ZONE scale.Otherwise the ground track line 238 will be lost beyond the laterallimits of the map 20 in the NEAR ZONE.

Once in the NEAR ZONE, the pilot marks at least once more before thepull-up maneuver. At one mile from the computed pull-up point 12, thegreen alert light 193 flashes. At two-thirds of a mile from the pull-uppoint 12, a second Warning is given by the same light 193. At this pointthe pilot should begin to level the wings of the aircraft 10. Atone-third of a mile from the pull-up point 12, the presentation on thevertical pointer 168 is changed from steering angle a to a combinedsignal of yaw and roll error. The horizontal pointer 176, which washorizontal just prior to the one-third mile point, drops abruptly andbegins to rise gradually toward the horizontal position as the pull-uppoint 12 is approached. This rise represents a visible warning of thepull-up point 12. Between the one-third mile point and the pull-uppoint, the pilot should depress the pickle button 236. When thehorizontal pointer 176 reaches zero, this signifies to the pilot hisarrival at the computed pull-up point. In addition, the red indicatorlight 206 is turned on and an oral tone is presented to the pilotthrough the earphones 207. From this point on, the horizontal pointer176 presents a programmed pull-up in terms of g-error. The accelerationtransition in the illustrated example in FIG. 1 from one to four gsfollows a negative cosine function of the ground distance traveled fromthe pull-up point 12. The four g-level is reached at a point which isabout one-third of a mile after the pull-up point 12. Therefore, thepilot must apply full throttle and pull back on the control stick toaccelerate the airplane in accordance with the programmed G schedule. Solong as the pilot keeps the horizontal pointer 176 horizontal, he isproperly controlling the transverse acceleration forces. Maintaining thevertical pointer 168 in a vertical position, thereby maintaining thewings of the aircraft 10 level during the pull-up, is imperative for anaccurate bomb delivery.

During the pull-up maneuver, bomb release is automatically effected bythe bomb release angle unit 210 Without any attention from the pilot.However, bomb release may be signaled to the pilot by the red light 206going out and the aural tone stopping. After bomb release, the yaw-rollindication is preserved until the pickle button 236 is released. Thepilot then continues on an inside loop and half-roll to maneuver theaircraft away from the target T.

It will be observed that during the run-in phase and the pull-upmaneuver, the pilot is presented with certain information. As a resultof operation on monitored inputs plus pilot corrections, the computersystem computes and W t IS a GOntinuous track of the instantaneous mapposition on the display unit 26. The knowledge of the present positionin relation to terrain features shown on the map 20 is very helpful forthe recognition of corresponding terrain features on the ground,particularly of the check points 1, 2, 3, 4 and 5. Obstacle avoidance isanother benefit of tracking information. The knowledge of presentposition in relation to future positions is also useful navigationalinformation. For example, if the trend of the successive map positionsforetells of possible entrance into the shaded area 21 on the map 20,the pilot can take appropriate action to avoid that area. Within theNEAR ZONE, the curved lines 22 guide the pilot into the region where theballistic computations are valid. If the ground track indicates itspossible intersection with one of these lines, the pilot knows that thisintersection is the last point along that particularly ground track fromwhich he could maneuver by two successive standard rate turns into theregion where the ballistic computation is valid.

Another type of information to the pilot is the steering angle a. Thesteering angle a is presented on the vertical pointer 168 of theindicator 170 from the start point S up to one-third of a mile frompull-up point 12. Thus, the steering angle 17 presents valuable guidanceinformation to the pilot for directing the aircraft to the target T; andat one-third of a mile from pull-up the indicator 170 is responsive tothe yaw and roll to aid the pilot in leveling the wings of the aircraft10.

The apparatus of the present invention has novel features which departfrom devices heretofore used in lowaltitude loft-bombing techniques.Several of the important features of the navigational computer may benoted, such as a moving-map type of navigational aid which includesample check points to eliminate the high dependence upon a singleinitial point, continuous ground tracking of the map position, steeringto a target within a relatively wide approach corridor, and permissibleWide variations in aircraft run-in speeds. The ballistic computeraffords a variable pull-up point dependent upon a variable run-in speedand range wind, a programmed transition of transverse accelerationduring pull-up, and a modification of the bomb release angle based ondeviations in fall-off of velocity from the ideal to compensate forvarious errors accumulated after pull-up. Due to these features thelowaltitude loft-bombing technique has been improved over the currenttechniques to the extent of greater reliability and accuracy of deliveryof the bomb on a target, greater flexibility in maneuvering of theaircraft, and less demand on pilot skill and acuity.

It will be understood that various changes in the details, materials,steps and arrangement of parts, which have been herein described andillustrated in order to eX- plain the nature of the invention, may bemade by those skilled in the art within the principle and scope of theinvention as expressed in the appended claims.

What is claimed is:

1. A variable pull-up point computer for use in a loftbombing mission byan aircraft, comprising:

first multiplier means having one input responsive to range windvelocity and another input responsive to the predicted time from pull-upof the aircraft to impact of the bomb,

a first differential means having one input connected to the output ofsaid multiplier means and another input responsive to the still-airpull-up distance,

second differential means having one input responsive to the groundspeed of the aircraft and another input connected to the output of saidfirst differential means,

first connecting means for intermittently connecting to the outputthereof an aircraft ground speed signal and operatively connected to theoutput of said second differential,

second connecting means for intermittently connecting the output thereofto a power source and operatively 1% connected to the output of saidfirst connecting means, and pull-up indicating means connected to theoutput of said second connecting means; whereby a command signal ispresented to the pilot at the correct pull-up point.

2. A variable pull-up point computer for use in a loftbombing mission byan aircraft, comprising:

computing means having inputs responsive to range wind velocity, thepredicted time from pull-up to impact and the still-air pull-updistance,

differential means having one input responsive to the ground speed ofthe aircraft and another input connected to the output of said computingmeans,

first connecting means for intermittently connecting to the outputthereof an aircraft ground speed signal and operatively connected to theoutput of said differential,

second connecting means for intermittently connecting the output thereofto a power source and operatively connected to the output of said firstconnecting means,

and pull-up indicating means connected to the output of said secondconnecting means;

whereby a command signal is presented to the pilot at the correctpull-up point.

3. A variable pull-up point computer for use in a 10ftbombing mission byan aircraft, comprising:

computer means having inputs responsive to range wind velocity, thepredicted time from pull-up point to impact, the still-air pull-updistance and the ground speed of the aircraft,

connecting means for intermittently connecting the output thereof to apower source and operatively connected to the output of said computermeans,

and signal indicating means connected to the output of said connectingmeans;

whereby a command signal is presented to the pilot at the correctpull-up point.

4. A pull-up program computer for use in a loft-bombing mission by anaircraft, comprising:

first multiplier means having one input responsive to range windvelocity and another input responsive to the predicted time from pull-upof the aircraft to impact of the bomb,

a first differential means having one input connected to the output ofsaid multiplier means and another input responsive to the still-airpull-up distance,

a second differential means having one input respon sive to the groundspeed of the aircraft and another input connected to the output of saidfirst differential means,

connecting means for intermittently connecting to the output thereof anaircraft ground speed signal and operatively connected to the output ofsaid second differential means,

scheduling means having an input connected to the output of saidconnecting means,

comparator means having one input operatively connected to the output ofsaid scheduling means and another input responsive to the verticalacceleration of the aircraft,

and indicating means for programmed pull-up having its input connectedto the output of said comparator;

whereby a command signal is presented to the pilot of the correctvertical acceleration program for pullup,

5. A pull-up program computer for use in a loftbombing mission by anaircraft, comprising:

first computing means having inputs responsive to range wind velocity,the predicted time from pull-up to impact and the still-air pull-updistance,

a differential means having one input responsive to the aircraft groundspeed and another input connected to the output of said first computingmeans,

connecting means for intermittently connecting to the output thereof anaircraft ground speed signal and operatively connected to the output ofsaid differential means,

second computing means having an input connected to the output of saidconnecting means and another input responsive to the verticalacceleration of the aircraft,

and indicator means for programmed pull-up having its input connected tothe output of said second computing means;

whereby a command signal is presented to the pilot of the correctvertical acceleration program for pull-up.

6. A pull-up program computer for use in a loftbombing mission by anaircraft, comprising:

first computing means having inputs responsive to range wind velocity,the predicted time from pull-up to impact, the still-air pull-updistance and the ground speed of the aircraft,

connecting means for intermittently connecting to the output thereof anaircraft ground speed signal and operatively connected to the output ofsaid first computing means,

second computing means having an input connected to the output of saidconnecting means, and another input responsive to the verticalacceleration of the aircraft,

and indicating means for programmed pull-up having its input connectedto the output of said second computing means;

whereby a command signal is presented to the pilot of the correctvertical acceleration program for pull-up.

7. A variable bomb release angle computer for use in a loft-bombingmission by an aircraft, comprising:

first multiplier means having one input responsive to range windvelocity and another input responsive to the predicted time from pull-upof the aircraft to impact of the bomb,

a first differential means having one input connected to the output ofsaid multiplier means and another input responsive to the still-airpull-up distance,

a second differential having one input responsive to the ground speed ofthe aircraft and another input connected to the output of said firstdifferential means,

first connecting means for intermittently connecting to the outputthereof an aircraft ground speed signal and operatively connected to theoutput of said second differential,

second connecting means for intermittently connecting the output thereofto a power source and operatively connected to the output of said firstconnecting means,

third connecting means for intermittently connecting the true air-speedof the aircraft at the output thereof and operatively connected to theoutput of said second connecting means,

fourth connecting means having an input for receiving a time signal andfor intermittently connecting said time signal at the output thereof,

first converting means having an input connected to the output of saidfourth connecting means for producing a predicted aircraft velocityfall-off signal at the output thereof,

third differential means having one input connected to the output ofsaid third connecting means and the other input connected to the outputof said first converting means,

second converting means having an input connected to the output of saidthird differential means for producing a bomb release correction angleat the output thereof,

fourth differential means having one input connected to the output ofsaid second converting means and another input responsive to apreselected bomb release angle,

fifth differential means having one input connected to the output ofsaid fourth differential means and the other input responsive to theaircraft pitch angle,

and bomb release means for releasing the bomb having the input thereofconnected to the output of said fifth differential means;

whereby the bomb will be released at a corrected bomb release angle.

8. A variable bomb release angle computer for use in a loft-bombingmission by an aircraft, comprising:

computing means having inputs responsive to range Wind velocity, thepredicted time from pull-up to impact, the still-air pull-up distanceand the ground speed of the aircraft,

first connecting means for intermittently connecting to the outputthereof an aircraft ground speed signal and operatively connected to theoutput of said computing means,

second connecting means for intermittently connecting the output thereofto a power source and operatively connected to the output of said firstconnecting means,

third connecting means for intermittently connecting the true air-speedof the aircraft and a time signal at separate outputs thereof andoperatively connected to the output of said second connecting means,

first converting means having an input connected to the time signaloutput of said third connecting means for producing a predicted aircraftvelocity fall-off signal at the output thereof,

first differential means having one input connected to the trueair-speed output of said third connecting means and the other inputconnected to the output of said first converting means,

second converting means having an input connected to the output of saidfirst differential means for producing a bomb release correction angleat the output thereof,

second differential means having one input connected to the output ofsaid second converting means and other inputs responsive to apreselected bomb re lease angle and the aircraft pitch angle,

and bomb release means for releasing the bomb having the input thereofconnected to the output of said second differential means; I

whereby the bomb will be released at a corrected bomb release angle.

9. A variable bomb release angle computer for use in a loft-bomb missionby an aircraft, comprising:

first computing means having inputs responsive to range wind velocity,the predicted time from pull-up to impact, the still-air pull-updistance and the ground speed of the aircraft,

first connecting means for intermittently connecting the output thereofto a power source and operatively connected to the output of said firstcomputing means,

second connecting means for intermittently connecting the true airspeedof the aircraft and a time signal at separate outputs thereof andoperatively connected to the output of said first connecting means,

second computing means having an input connected to the output of saidsecond connecting means for producing a bomb release angle correctionsignal at the output thereof,

differential means having one input connected to the output of saidsecond computing means and the other input responsive to a preselectedbomb release angle and the aircraft pitch angle,

and bomb release means for releasing the bomb having the input thereofconnected to the output of said differential means;

whereby the bomb will be released at a corrected bomb release angle.

10. A ballistic computer for use in a loft-bombing mission by anaircraft, comprising:

computing means having an output indicative of the distance to apreselected target,

means responsive to the true airspeed of the aircraft for providing anoutput signal proportional to the actual integrated true airspeed,

means operatively connected to said true airspeed responsive means forproviding an output signal proportional to the aircraft ground speed,

means for providing a signal indicative of a predicted integrated trueairspeed under still-air conditions as a function of the integratedaircraft ground speed,

first differential means for combining the actual and the predictedintegrated true airspeeds and having an output indicative of range Winddistance error,

second differential means for combining said distance error with saiddistance to the target thereby providing a corrected distance to thetarget at the output thereof,

g-programmer means selectively connected to said computing means forproviding an output signal indicative of a scheduled transverseacceleration of the aircraft,

means responsive to the output of said second differential means forconnecting said g-programmer means to said computer means,

alerting means operatively connected to the output of said seconddifferential for providing a pull-up signal to the pilot,

a bomb release means having inputs responsive to the true airspeed, timeand pitch of the aircraft and having an output indicative of computedrelease angle, and

a bomb release rack adapted to be attached to the aircraft and having aninput connected to said release means output for effecting bomb release.

11. A ballistic computer for use in a loft-bombing mission 'by anaircraft, comprising:

computing means having an output indicative of the distance to aselected target,

means responsive to the true airspeed of the aircraft for comparing theactual integrated true airspeed with a predicted integrated trueairspeed under stillair conditions and providing an output indicative ofrange wind distance error,

differential means for combining said distance error with said distanceto the target thereby providing a corrected distance to the target atthe output thereof,

g-programmer means selectively connected to said computing means forproviding an output signal indicative of a scheduled transverseacceleration of the aircraft,

means responsive to the output of said differential means for connectingsaid g-programrner means to said computing means,

alerting means operatively connected to the output of said differentialfor providing a pull-up signal to the pilot,

and a bomb release means having inputs responsive to the true airspeed,time and pitch of the ai craft and having an output indicative ofcomputed release angle, and

a bomb release rack adapted to be attached on the aircraft and having aninput connected to said release means output for effecting bomb release.

12. A ballistic computer for use in a loft-bombing mission by anaircraft, comprising:

computing means having an output indicative of the distance to aselected target,

means responsive to the actual true airspeed of the aircraft forcomparing the actual integrated true airspeed with a predictedintegrated true airspeed under still-air conditions and providing anoutput indicative of range wind distance error,

differential means for combining said distance error With said distanceto the target for providing a corrected distance to the target at theoutput thereof,

alerting means operatively connected to the output of said differentialfor providing a pull-up signal to the pilot,

a bomb release means having inputs responsive to the true airspeed, timeand pitch of the aircraft and having an output signal adapted foractuating a bomb rack to release a bomb thereon.

References Cited UNITED STATES PATENTS 2,791,766 5/1957 Luck 235-6152,825,055 2/1958 Chance 235-615 X 2,988,960 6/1961 Helgeson et al.235-615 X 3,070,307 12/1962 Helgeson et al. 235-15026 3,088,372 5/1963Brink et a1. 235-615 X 3,091,993 6/1963 Brink et a1. 89-15 MALCOLM A.MORRISON, Primary Examiner. I. KESCHNER, J. RUGGIERO, AssistantExaminers.

